A hull of a boat resting in a body of water tends to become plated with organic and other contaminants. Such plating can be unsightly, damaging to the boat, and serve to reduce the boat's operating efficiency.
In order to mitigate such plating, it is known to elevate boats, especially smaller pleasure craft, out of the water when not in use. Various forms of boat lift have been developed for this purpose. Such boat lifts typically include a base that rests on and/or is anchored to the bottom of the body of water, for example, to a lake bottom, an elevatable portion or cradle configured to support the hull of a boat, and a mechanism configured to raise and lower the cradle with respect to the base.
One such mechanism involves a cable and pulley arrangement wherein displacement of the cable in a first direction raises the cradle and displacement of the cable in a second direction lowers the cradle. The cable may be displaced in the first direction by winding it onto a spool, and the cable may be displaced in the second direction by unwinding it from the spool. The spool may be driven by a hand wheel operating through a gear box. This type of mechanism is relatively simple and inexpensive, but it can be require considerable time and effort to operate. Also, the cable and pulleys are susceptible to damage and wear through use and corrosion through contact with the environment, including the water in which the boat lift is installed.
Another such mechanism involves one or more hydraulic actuators, each having a cylinder and piston rod, connected between the base and the cradle and a hydraulic pump and controller for operating the actuator(s). This type of mechanism is relatively easy to operate, but typically is much more expensive than a cable and pulley-type of boat lift. Also, such mechanisms typically are configured with the actuator below the water line so that the actuator piston rod is extended from the actuator cylinder when the cradle is in the elevated position (where it typically spends the great majority of its time). As such, the piston rod is susceptible to corrosion and plating of contaminants thereon. Such corrosion and plating can damage the seal between the piston rod and cylinder and lead to leakage of hydraulic fluid out of the actuator. This can diminish the performance of the actuator and pollute the environment in which the boat lift is installed.